Downhole valve device

ABSTRACT

A downhole valve device ( 1 ) in a drill string ( 14 ) in a petroleum well ( 2 ) and method for maintaining optimal annular fluid velocity and wellbore pressure. The device comprises a valve housing ( 20 ) connected between adjacent segments ( 12, 13 ) of the drill string. The valve housing is further provided with at least one valve ( 23 ) arranged to open and close to the flow of drilling fluid based on measured values of downhole physical parameters or on signals from the surface in order to permit the through-flow of a sufficient volume of drilling fluid necessary to adjust and maintain the annular fluid velocity of the drilling fluid and the wellbore pressure within optimal operating conditions.

BACKGROUND OF THE INVENTION-FIELD OF THE INVENTION

This invention relates to a downhole valve to be installed in a drillstring, of the kind used for example in the exploration and recovery ofpetroleum deposits. In particular the invention relates to a downholevalve and method for adjusting and maintaining annular fluid velocity ofthe drilling fluid within optimal levels.

BACKGROUND OF THE INVENTION-DESCRIPTION OF RELATED ART

In petroleum wells it is common practice to case down to a certain welldepth in order, ia., to ensure that the well will not collapse. From thelower end portion of the casing an uncased well section of a smallerdiameter is drilled further into the formation. The transition betweenthe casing and the uncased well is commonly referred to as a “shoe”, inthe following referred to as a “transition shoe”. Drilling fluid (mud)is pumped from the surface down the drill string to the drill bit inorder to cool and clean it. The drilling fluid returns together withsevered cuttings to the surface through the annulus formed between thedrill string and the wall of the well. During drilling there is the riskthat the cuttings may settle from the drilling fluid and accumulatealong the low side of the well profile, which entails the risk of thedrill string jamming. It is therefore very important that drilling fluidis supplied in an adequate amount for such settling to be avoided. Bysettling is meant, in this connection, that particles fall out of afluid mixture. At the transition shoe between the cased and the uncasedpart of the well, there is an increase in pipe diameter which makes thedrilling fluid flow at a reduced rate because of the cross-sectionalincrease. Settling of cuttings from the drilling fluid often occurs inthis region. In long wells, by high drilling fluid velocity there willalso be a considerable flow resistance in the drilling fluid. Therefore,in order to achieve the desired amount of flow, the pump pressure mustbe increased. However, other drilling-technical conditions set limits tohow high or how low a pressure may be used. For example, drilling fluidmay enter the well formation by too high a pressure. By to low apressure the wall of the well may collapse, or well fluid may enter fromthe well formation into the well, which may result in an uncontrollabledrilling situation. A typical well profile penetrates a number offormation strata of different geological properties. The estimated porepressure and fracture limits of the formations drilled set limits to thespecific gravity of the drilling fluid. As longer wells are beingdrilled, the problems become more pronounced.

The main portion of time loss occurring during drilling may be ascribedto these conditions and other hydraulically related problems, such asthey will be described in the following, and to the measures that haveto be taken to control them.

According to known technique, the above-mentioned tasks are solved byutilizing a number of different methods and measures. The well pressureis controlled essentially by adjusting the specific gravity, rheologicalproperties and pressures of the drilling fluid.

The settling of cuttings from the drilling fluid may be reduced and holecleaning improved by increasing the rotational speed of the drillstring. The drilling fluid is then drawn along into a rotary motion inaddition to the axial movement. This results in a helical flow whichcauses a higher flow rate because the flow path is longer than by axialmovement only. Good cleaning may also be achieved by running the drillstring slowly up and down at the same time as drilling fluid is flowingthrough the well.

When, due to too high pressure, drilling fluid penetrates the wellformation, a substance may be added, which will tighten the pores of thewell, e.g. crushed nutshell. The specific gravity of the drilling fluidmay also, perhaps at the same time, be lowered to reduce the pressureand thereby prevent further fracturing.

In a so-called “kick” gas is flowing from the well formation into thewell displacing drilling fluid. This results in more drilling fluidflowing out of the well than being supplied. Such a potentialuncontrollable situation is countered by pumping down heavier well fluidinto the well. This is a slow process because the gas expands further asit is rising within the well and the hydrostatic pressure is reduced.Circulating gas out from the well may typically take 24 to 48 hours.

The reason for the drawbacks of known technique is primarily that it isdifficult and often not possible to adjust the properties of thedrilling fluid an such a way that it will meet the most importantdrilling-technical requirements within the restrictions set by theformation. In longer wells the loss of flow friction of the drillingfluid contributes to the fact that the difference in pressure of thedrilling fluid when it is being pumped through the well (total pressure)and when it is not in motion (static pressure) becomes greater. Thismakes it difficult to keep the well pressure within the limits set bythe pore pressure and fracture limit of the formation. Thus, it is notpossible to use a total pressure that will provide the desires flow ratein the drilling fluid, which results in increasing settling of cuttingsfrom the drilling fluid, in particular at the transitions between thecased and the uncased well portions.

BRIEF SUMMARY OF THE INVENTION

The invention has as its object to remedy the negative aspects of knowntechnique.

The object is realized according to the invention through the featuresset forth in the description below and in the subsequent claims.

At a distance from the drill bit, which distance is adjusted inaccordance with the well conditions, and which may typically be severalhundred meters, one or more downhole valves are installed, which arearranged to direct part of the drilling fluid flowing down through thedrill string, out into the annulus between the drill string and thecasing/formation wall.

The downhole valve may comprise a valve housing with a built-in valve, adistributor housing and necessary control components. The downhole valveis provided with securing devices complementarily matching the threadedpipe. connections of the drill string, and is secured between adjacentpipe sections. The downhole valve forms an integrated part of the drillstring. An axial bore extending through the valve housing allows thedrilling fluid to flow freely between the two connected drill pipesthrough the valve housing. The downhole valve is arranged to open/closea connection between the internal axial bore and an annular distributorhousing. When the distributor housing is not installed, the openingopens directly into the annulus around the downhole valve. Thedistributor housing encircling the valve housing is provided withopenings/slots distributed round the periphery of the distributorhousing. The opening(s) is (are) arranged to distribute the exitingdrilling fluid approximately equally round the downhole valve.

The valve is arranged to open and close during drilling, by means of anactuator and a control system of a kind known in itself. For example, anelectric actuator may be controlled to open and close the valve wheneverpre-programmed physical parameters are met. Such planters may be wellangle and/or well pressure. The valve may be overridden, for example, bythe drill string being rotated at specific speeds in a predeterminedsequence, or by acoustic communication to the surface.

In a typical drilling situation, in which there is a risk that cuttingswill settle from the drilling fluid, in particular at the transitionbetween cased and uncased well, and in which it is not convenient toincrease the pump pressure or the specific gravity of the drilling fluidfurther because of the risk of drilling fluid entering the formation,the valve is opened and a portion of the drilling fluid, which isflowing down the drill string, flows out into the annulus. The flow ofdrilling fluid in the upper part of the well may thereby be increasedwithout the pressure increasing correspondingly. The velocity of thedrilling fluid in the annulus between the drill string and the casingincreases and settling of cuttings from the drilling fluid may beprevented.

By unwanted inflow of gas or liquid from the formation into the well, itis possible to open the valve and thereby quickly pump down heavierdrilling fluid which then intersects the gas pocket or the formationliquid which is entering the well. Correspondingly, by unwanted outflowof drilling fluid to the formation because of overbalance in the fluidpressure, the downhole valve may be opened and lighter drilling fluid bepumped directly into the annulus above the leakage area to remedy thissituation.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following will be described a non-limiting example of a preferredembodiment visualized in the accompanying drawings, in which:

FIG. 1 shows schematically in section a well, in which a drill string,with a downhole valve according to the invention installed, is placed ina well bore; and

FIG. 2 shows in section and in part schematically a down hole valve indetail.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings the reference numeral 1 identifies a downhole valveaccording to the invention, see FIG. 1. In a well 2 a casing 3 has beenlowered into the part initially drilled. The casing 3 ensures that thewell does not collapse, and thereby forms an appropriate shaft fordrilling to be continued into the uncased part 4 of the well. In thetransition between the cased and uncased parts of the well is disposed atransition shoe 5 forming a transition between the relatively largediameter of the casing 3 and the smaller diameter of the uncased wellpart 4. The downhole valve 1 is connected between two drill pipes 12 and13 and form part of a drill string 14. The downhole valve 1 is builtinto the drill string 14 at a distance, adjusted according to the wellconditions, from the lower end portion 15 of the drill string 14, towhich the drill bit 16 is attached.

At its two end portions a valve housing 20 of the downhole valve 1 isprovided with securing devices 21, 21′ complementarily matching thethreaded connectors 12′ and 13′ of the drill pipe, see FIG. 2. In thevalve housing 20 there is a bore 22 extending therethrough and forming aconnection between the pipes 12 and 13. A valve 23, which may possiblycomprise several valves, is disposed in the valve housing 20 between thebore 22 and an annulus 24 formed between the valve housing 20 and adistributor housing 25. In this connection the valve 23 may possiblycomprise several volume flow controlling devices. The periphery of thedistributor housing 25 is provided with openings in the form of one oremore holes/slots 26 arranged to distribute the exiting drilling fluidapproximately equally round the valve housing 20. The downhole value 1will also work without the distributor housing 25. The valve 23 isopened and closed by an actuator 27. In a preferred embodiment theactuator 27 is operated electrically by a control device 28, batteries29, sensors 30 and electrical cables 31. The valve 23, actuator 27 andthe electrical control means 28 to 31 are all of embodiments known inthemselves, and may be controlled, for example, in that the sensors 30measure value, for example pressure or angular deviating exceeding apredetermined value. The values are communicated to the control device28 which outputs a signal through electrical cables 31 to the actuator27 opening the valve 23.

In a typical work situation drilling fluid is pumped down through therotating drill string 14 out through several openings 17 in the drillbit 16. The drilling fluid cools the drill bit 16 and at the same timewashes away the drilled cuttings. Well fluid and cuttings then returntowards the surface through an annulus 4′ formed between the drillstring 14 and the well formation, and then further at reduced velocitydue to the increase in diameter, through an annulus 3′ formed betweenthe drill string 14 and casing 3. As drilling proceeds and the length ofthe uncased well part 4 increases, the pressure of the drilling fluidmust also be increased in order for the increased flow resistance to beovercome. At a specific pressure the drilling fluid will enter theformation and make it possible to maintain the same flow rate. Thus,according to known technique, the rate of the drilling fluid will haveto be reduced, which makes settling of cuttings from the drilling fluidincrease, especially at the transition shoe 5 where there is a reductionvelocity. By opening of the valve 23 of the downhole valve 1, drillingfluid will exit the drill string 14 into the annulus 3′ upstream of thedrill bit. The drilling fluid flow rate may then be increased without anincrease in the pressure worth mentioning, and settled cuttings areswept along by the drilling fluid and carried out of the well bore. Asthe downhole valve 1 is displaced past the transition shoe 5 into theuncased part 4 of the well, another downhole valve 1 which is positionedfurther up in the drill string 14 may open. The first downhole valve 1may, if desired, be closed autonomously or from the surface.

The downhole valve enables a relatively quick out-circulation, andchange of the specific gravity, of the drilling fluid at the upperportion of the well. This is of great importance when undesiredsituations arise in the well, with well fluid entering the well, or whendrilling fluid enters the formation. As described above, the downholevalve is operative during the entire drilling operation and may beopened and closed any time without this causing interruption to thedrilling itself.

A valve according to the invention will considerably improve thecontrollability of the hydraulic situation in a well, while at the sametime the time for handling known well problems is reduced.

1. A downhole valve device (1) in a drill string (14) in a petroleum well (2) for adjusting the annular fluid velocity and wellbore pressure, comprising a valve housing (20) having connection means for connecting the valve housing between adjacent segments (12, 13) of the drill string, the valve housing further comprising a longitudinal bore (22) forming an unimpeded fluid connection between the adjacent segments, the valve housing (20) being provided with at least one valve (23), located between longitudinal bore (22) and an annulus (3′, 4′) between the well (2) and the drill string (14), the valve (23) being caused to open and close to the flow of drilling fluid from the longitudinal bore (22) to the annulus (3′, 4′) between the well (2) and the drill string (14) by an actuator (27), said actuator (27) responding to a control device (28) connected to a sensor (30) that detects changes in downhole physical parameters or signals from the surface, the valve (23) of the downhole valve device (1) being further provided with means to permit even distribution of drilling fluid into the annulus.
 2. The device according to claim 1, wherein the means for permitting even distribution of drilling fluid comprises a cylindrical distributor housing (25) having a plurality of openings (26) distributed along its periphery, said distributor housing being arranged coaxially with drill string (14) so as to form an annulus (24) between valve housing (20) and distributor housing (25) such that the fluid flowing through the valve (23) will enter annulus (24) and be evenly distributed into the well bore through openings (26).
 3. A method for adjusting annular velocity of drilling fluid and well bore pressure in a petroleum well having a drilling string, the method comprising the steps of: a. determining a desired range of annular velocity and pressure of the drilling fluid for a given well formation or drilling condition, b. actively measuring changes in the physical parameters in the well, c. venting, by the use of a valve device according to either of claims 1 or 2, in response to a detected change in the physical parameters in the well, or in response to a predetermined event, a sufficient volume of drilling fluid from inside the drilling string to an annulus formed between the drilling string and the well bore, for a sufficient amount of time, so as to adjust and maintain the annular velocity of the drilling fluid and the well bore pressure within the desired range.
 4. The method according to claim 3, whereby the valve device is arranged in the drilling string at the vicinity of the drill bit.
 5. The method according to claim 4, wherein, in addition to the valve device arranged in the vicinity of the drill bit, a plurality of valve devices are arranged at intervals along the length of the drill string. 